Public health workers have a tremendous opportunity to help bring health coverage to all Americans. But data released Tuesday show that we must act fast.

A survey conducted by the Commonwealth Fundshows that the Affordable Care Act has brought health insurance to more than 50 percent of the 15 million young adults enrolled in a parent’s health plan in the past year. Unfortunately, only about one-fourth of young adults know about the Health Insurance Marketplace, which beginning Oct. 1 will be the new way for many Americans to acquire health coverage — including Medicaid and the Children’s Health Insurance Program.

The study suggests public health has an important role in the coming months: to educate young adults in all communities on how to use the new marketplace. According to the study, when Americans learned that the law allows young adults to stay longer on their family’s insurance plans, more young adults enrolled for coverage — from 13.7 million in November 2011 to 15 million in March 2013.

“There is a stereotype that young adults believe they are ‘invincible’ and don’t want or need health insurance,” said Sara Collins, Commonwealth Fund vice president. “This survey shows that is a myth; a typical uninsured young adult is from a low- or middle-income family and works a low-wage job. In general, young adults value health insurance but cannot afford it.”

While the Affordable Care Act’s expansion of the Medicaid program will help ensure the affordability of health insurance for some, the survey warns that the “major risk to young adults gaining health insurance … is the reluctance of many state governments to expand their Medicaid programs.”

Starting Oct. 1, Americans in every state can apply for health coverage online, by mail or in person. However, many Americans likely will not use the Marketplace without intervention. According to the Commonwealth survey, “one-third of college graduates were aware of the marketplaces, compared to 20 percent of those with a high school degree or less.”